1. Field of the Invention
This invention relates to a process for refining copper-containing mattes by blowing such mattes with an oxidizing gas rich in oxygen while injecting a cooling agent peripherally of the oxidizing gas.
2. Description of the Prior Art
It is well known that copper matte can be converted to copper metal (in an impure form known as "blister" copper) by oxidizing the iron and sulfur contained in the matte. The conversion is commonly carried out in a horizontal, rotating cylindrical furnace known as a Pierce-Smith converter. This converter has a basic refractory lining, usually of magnesia, with tuyeres embedded in the refractory for introducing blasts of air or oxygen-enriched air into the molten copper matte from beneath its surface. The blast blown through the tuyeres, which consist of single tubes, cannot be enriched beyond about 36% of oxygen without causing rapid erosion of the turyeres and the surrounding refractory. Even in observing this maximum oxygen content of the blast, refractory consumption in the Pierce-Smith converter is relatively high; for example, in the range of 2 to 5 kg per ton of copper refined.
Conventional copper matte refining processes present other operating problems, one of which being proper control of the matte temperature during refining. In the conversion of copper matte by blowing with an oxidizing gas, it is known that the matte temperature must be maintained between 1220.degree. C and 1350.degree. C. Below 1220.degree. C, the slag formed during the process is too pasty for proper working and removal. If, on the other hand, the matte temperature exceeds about 1350.degree. C, the refractory lining of the converter, particularly in the tuyere zones, is worn too rapidly.
Maintenance of the temperature within this relatively narrow range (about 130.degree. C) is complicated by the required refining procedures; namely, that the refining operation must be interrupted at intervals to remove slag and introduce further amounts of matte and other additions into the converter. Such an interruption, coupled with the addition of matte which may often be cool, causes the temperature of the molten furnace charge to tend toward the low side of the practical working temperature range of 1220.degree. C to 1350.degree. C. It is well known, of course, that such lower temperatures favor the formation of magnetite (Fe.sub.3 O.sub.4) as a result of the oxidation of iron sulfide (FeS).
The presence of magnetite in the molten bath has a further chilling effect on the matte, so the formation of magnetite and its deposition on the refractory lining is to be minimized from the standpoint of heat balance. Furthermore, the deposited magnetite tends to gradually clog the tuyeres, particularly at the relative low blowing pressures used in conventional processes; this necessitates periodic unclogging of the tuyeres by pushing rods through them during periods when blowing is stopped.
Magnetite formation poses additional problems for the operator. For example, magnetite tends to thicken the slag and thereby cause the well-known operating difficulties associated with a thickened slag. Magnetite production also tends to increase the copper content of the slag with a corresponding reduction in yield. Magnetite formation is especially prevalent where copper-rich mattes (i.e. those containing 60% copper or more) are to be refined because the iron content of such mattes is relatively low and the heat balance of the operation is correspondingly less desirable. Of course, the formation of magnetite and the attendant reduction in bath temperature result in other unfavorable process conditions such as the difficulty encountered in removing elements like arsenic and bismuth from the matte.
Even though workers in the art may have recognized the desirability of carrying out the conversion of copper mattes in a temperature range higher than theretofore attainable, the attempts to reach higher temperatures have been limited to such well known expedients as localized heating of the converter lining, for example with an oxyfuel lance, when blowing is stopped; this technique, however, does not really address the problem because the heating step does not occur simultaneously with the refining operation.